Benthic Habitats and the Effects of Fishing

The Impact of Trawling on Benthic Nutrient Dynamics in the North Sea: Implications of Laboratory Experiments

Phil Percival, Chris Frid, and Rob Upstill-Goddard

doi: https://doi.org/10.47886/9781888569605.ch72

Abstract. The effects of trawling on North Sea sediment nutrient dynamics were quantified in microcosm experiments. North Sea sediments were collected from a fishing ground and placed into a series of nine microcosm systems. Following a stabilization period, simulated trawling events employed at moderate (trawled every other day) and heavy (trawled every day) trawl frequencies were compared to untrawled control systems. Nutrient concentrations (nitrite, nitrate, ammonium, and phosphate) were measured periodically over 98 h and resultant fluxes calculated. Trawl impact effected all the measured nutrient species. Flux rate changes following a trawl event persisted between trawl events (i.e., >48 h), and instantaneous fluxes exhibited the same basic pattern irrespective of the history of trawling. This implies that in regularly fished areas of the North Sea, nutrient dynamics may be in a permanently altered state, with enhanced fluxes of ammonium and phosphate. It is concluded that the impact of trawling and subsequent alteration to the benthic nutrient dynamic is potentially a globally significant impact on coastal nutrient dynamics and primary production.